Effects of degassing on the long-range attractive force between hydrophobic surfaces in water

The long-ranged attractions between hydrophobic amorphous fluoropolymer surfaces are measured in water with and without dissolved air. An atomic force microscope is used to obtain more than 500 measured jump-in distances, which yields statistically reliable results. It is found that the range of the attraction and its variability is generally significantly decreased in deaerated water as compared to normal, aerated water. However, the range and strength of the attraction in deaerated water remain significantly greater than the van der Waals attraction for this system. The experimental observations are consistent with (1) nanobubbles being primarily responsible for the long-ranged attraction in normal water, (2) nanobubbles not being present in deaerated water when the surfaces are not in contact, and (3) the attraction in the absence of nanobubbles being most probably due to the approach to the separation-induced spinodal cavitation of the type identified by Bérard et al. [J. Chem. Phys. 1993, 98, 7236]. It is argued that the measurements in deaerated water reveal the bare or pristine hydrophobic attraction unobscured by nanobubbles.     

Temperature effects on the carbon-13 NMR shifts of selected compounds

The effects of temperature on the ¹³C NMR shifts of benzene, cyclohexane, pyridine, cyclohexene, neopentane, hexane, and heptane have been determined from +10 to +70°C. In addition, the temperature shift of ²D in D₂O was found to be +10.4 × 10^?3 ppm/°C. All shifts appear to be linear functions of temperature within experimental error.     

Annulation of primary amines to piperazines and diazaspirocycles utilizing alpha-methyl benzyl resin

The microwave-assisted solid-phase synthesis of piperazines, 3,9-diazaspiro[5.5]undecanes and 2,9-diazaspiro[5.5]undecanes is reported. The synthesis relies on the direct annulation of primary amines with resin-bound bismesylates. Critical to the success of this chemistry was the development of alpha-methyl benzyl carbamate resin linker. This resin permits the cleavage of the heterocycles under mildly acidic conditions, free of contaminating linker-derived N-alkylated byproducts.     

Conformational properties of a phototautomerizable nucleoside biomarker for phenolic carcinogen exposure

We have characterized the conformational properties of the C8-deoxyguanosine (C8-dG) nucleoside adduct, 8-(2"-hydroxyphenyl)-2'-dG (1), which is a potential biomarker for exposure to phenolic carcinogens. Adduct 1 possesses the unique ability to phototautomerize, through an excited-state intramolecular proton transfer (ESIPT) process, to generate its keto form. This tautomerization depends on the presence of an intramolecular hydrogen (H)-bond between the phenolic OH and the imine nitrogen (N7) and has permitted insight into the equilibrium ground states of adduct 1. The results of our studies demonstrate that adduct 1 undergoes an ESIPT despite preferring a nonplanar "twisted" conformation that is imposed by the deoxyribose (dR) sugar moiety. Interestingly, a planar conformation of adduct 1 is also formed in certain aprotic solvents due to the anchoring effect of the intramolecular H-bond. Our results provide a basis for future studies aimed at determining the conformations of adduct 1 within DNA that will aid in our understanding of phenol-mediated carcinogenesis.     

Some observations on the substructure lattice of a Δ1 ultrapower

Given a (nontrivial) Δ₁ ultrapower ?/??, let ??_U denote the set of all Π₂‐correct substructures of ?/??; i.e., ??_U is the collection of all those subsets of |?/??| that are closed under computable (in the sense of ?/??) functions. Defining in the obvious way the lattice ??(?/??)) with domain ??_U, we obtain some preliminary results about lattice embeddings into – or realization as – an ??(?/??). The basis for these results, as far as we take the matter, consists of (1) the well‐known class of (non‐trivial) minimal ?/??'s, which function as atoms, and (2) the class of minimalfree ?/??'s, to whose nonemptiness a substantial section of the paper is devoted. It is shown that an infinite, convergent monotone sequence together with its limit point is embeddable in an ??(?/??), and that the initial segment lattices {0, 1,…, n } are not just embeddable in (as is trivial), but in fact realizable as, lattices ??(?/??). Finally, the diamond is (easily) embeddable; and if it is not realizable, then either the 1 ‐ 3 ‐ 1 lattice or the pentagon is at least embeddable (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Reconstructing supernova-neutrino spectra using low-energy beta beams

Neutrinos are the principal messengers reaching us from the center of a supernova. Terrestrial neutrino telescopes can provide precious information about the processes in the core of the star. But the information that a neutrino detector can supply is restricted by the fact that little experimental data on the neutrino-nucleus cross sections exist and by the uncertainties in theoretical calculations. In this Letter, we propose a novel procedure that determines the response of a target nucleus in a supernova-neutrino detector, by using low-energy beta beams. We show that fitting "synthetic" spectra, constructed by taking linear combinations of beta-beam spectra, to the original supernova-neutrino spectra reproduces the folded differential cross sections very accurately. Comparing the response in a detector to these synthetic responses provides a direct way to determine the main parameters of the supernova-neutrino energy distribution.     

Diamond Electrodes for High Sensitivity Mercury Detection in the Aquatic Environment: Influence of Surface Preparation and Gold Nanoparticle Activity

This work compares polished and unpolished boron doped diamond (BDD) electrodes decorated with two sizes of gold nanoparticles (AuNPs) for use as robust mercury sensors in aquatic environments. The size of the catalytically active AuNPs on the electrode surfaces was demonstrated to have a less significant effect on the sensitivity for mercury detection than the surface preparation of the BDD. The lowest limits of detection were achieved with the polished BDD electrodes, which both detected mercury at a concentration of 1 pM, six orders of magnitude greater sensitivity than the lowest detection limit of 5 μM achieved with an unpolished BDD electrode, and high in comparison with other reported electrode systems.